A variety of devices rely upon solenoid controlled apparatus. In automobiles, for example, various valves and electrical switches make use of solenoid controls which translate the motion or position of the solenoid armature to control position or state of valves or switches. Such devices are commonly referred to as solenoid controlled valves and relays, respectively. Many such devices assume a deenergized condition when current is removed from the solenoid and an energized condition when current is applied to the solenoid. The deenergized condition is characterized by a first armature position established by a bias spring acting upon the armature. The energized condition is characterized by a second armature position established by electromagnetic attraction of the armature to the solenoid core. In order that the second armature position is maintained, a holding current must continually be supplied to the solenoid lest the bias spring return the armature to the first armature position. Holding current is generally undesirable in automotive applications as such represents a source of electrical energy being dissipated out of an electrical system having severely limited electrical generation and storage capabilities. Additionally, integration of such devices embodied in relays onto printed circuit boards within various automotive or nonautomotive controllers has the additional shortfall of substantial heat generation resulting from ohmic losses of the solenoid which may preclude or limit such use or require special thermal management consideration.
Various mechanisms are known by which the necessity for holding current may be eliminated. Such mechanisms are generally referred to as latching mechanisms for their ability to retain an established position of state of a device. Magnetically latching solenoid devices are known which utilize permanent magnet force to latch an armature in one of two bistable conditions, the other bistable condition being latched mechanically by spring force. It has also been suggested to utilize permanent magnet force to selectively latch an armature in either of two bistable conditions. U.S. Pat. Nos. 4,737,750 and 5,272,458 for example show solenoid controlled apparatus including a permanent magnet coupled to an armature assembly and a single pole piece structure interacting with one pole of the permanent magnet. The pole piece is established at one of an aiding or opposing polarity with respect to the permanent magnet by way of opposite polarity flux established by an energized coil. Opposite polarity flux is established by bidirectional current delivery through a single coil or independent current delivery through a pair of oppositely wound coils. Bidirectional current delivery may require undesirably complex and costly driver circuitry while independent current delivery may require undesirably high coil mass, volume, and cost.
Additionally, as noted above in exposition of features of certain latching solenoid apparatus, a single pole piece interacts with the permanent magnet to effectuate state changes. The energy requirements between the two state changes may be very different owing to the different air gaps between the pole piece and magnet associated with each state. This changes the overall permeance of the magnetic circuit and may require substantially more flux to establish an attractive polarity than to establish an opposing polarity. This call for flux control may undesirably require various combinations of current delivery control such as by pulse width modulation depending upon the polarity desired, winding ratio other than unity between oppositely wound coils, and/or various performance and response trade-offs in toggling between states.
Inclusion of bias springs in the latching mechanism may also require substantial coil generated flux to counteract the spring force particularly in light of substantial air gaps and low permeance of the magnetic circuit in spring latched conditions. Additionally, inclusion of bias springs in the latching mechanism may also require substantial permanent magnet flux to counteract the spring force in magnetically latched conditions. Each of these shortfalls alone may undesirably add to mass, size and cost as attributable to larger coil(s), larger magnet, and /or high density permanent magnets.
Specifically with respect to relay applications, movable relay contacts pads are conventionally disposed at a distal end of a resilient conductor arm fixably coupled to the armature. As the armature is pulled toward the energized position against the solenoid coil a movable contact couples to a stationary contact and the resilient conductor yields under the attractive force between the armature and solenoid core until the armature motion is stopped by its contacting the core. Over time and cycles, the resiliency characteristics of the resilient conductor arm degrades and the contact pads wear, corrode and/or are consumed by arcing resulting in reduced contact force throughout the life of the relay. At the same time, arc erosion products formed on the surfaces of the contact pads are more resistive and require increased contact force to maintain low resistance across the contacts. Therefore, contact force reductions are undesirable since ohmic performance is positively correlated to contact force.